Syringes and syringe pumps

ABSTRACT

A medical syringe comprises a cylindrical barrel 1 having therein a plunger 4 which can be axially driven by a plunger rod 3. The plunger rod 3 passes through an aperture in the centre of a finger grip 2 having two finger grip projections 2b at opposite sides thereof. A data carrier means in the form of an electrically or magnetically operable device 2c is mounted near the end of one of the two finger grip projections 2b, with preferably a device 2c mounted near the end of each finger grip projection 2b. The device 2c carries data relating to the medicament contained or to be contained within the syringe, and can be read by a suitably adapted syringe pump when the syringe is mounted thereon to be driven by the syringe pump.

This application claims benefit of international applicationPCT/GB94/00909, filed Apr. 28, 1994.

This application claims benefit of international applicationPCT/GB94/00909, filed Apr. 28, 1994.

This invention relates to syringes and syringe pumps and moreparticularly, but not necessarily exclusively, to such devices appliedto the delivery of medicament, including anaesthetics, to medicalpatients.

Syringes have been in use for many years for delivering medicament,including anaesthetics, by doctors and nurses to medical patients, bothinside and outside hospitals. Originally, syringes were always operatedmanually by the doctor or nurse. Manual operation of a syringe is nothowever suitable where the medicament is to be delivered to the patientat an accurately controlled rate over a relatively long period of time.

A more recent development is that of the syringe pump, being a deviceupon which a syringe containing medicament can be mounted. The syringeis securely retained on the syringe pump, and the plunger rod of thesyringe is engaged by a drive device which can move in the axialdirection of the mounted syringe in order to deliver medicamenttherefrom. In some types of syringe pump the drive device is alinearly-acting member constrained to move in a straight line along thesyringe pump, whereas in other types of syringe pump the drive devicecan comprise a rotary screw cooperable with a fixed nut. When the screwis driven in rotation it cooperates with the fixed nut and moves axiallyto drive the syringe plunger rod.

Conventionally, the syringe is filled with medicament by the doctor ornurse and properly located on the syringe pump. The syringe pumpcomprises computer control means for controlling the syringe drivedevice and comprising a keyboard and display. The doctor or nurse canprogram the computer control means through the keyboard, setting forexample the continuous medicament flow rate which is required for theparticular patient concerned, and the duration of the infusion which isrequired.

DE-A-4020522 discloses a syringe pump wherein the flow rate can beinfluenced by the syringe size, indicated by means of the valve of aresistance incorporated in a syringe pump trough corresponding to aparticular syringe.

There is further disclosed in International Publication No. WO 91/04759a syringe pump which can operate with a syringe having a bar codethereon to program the computer control means with data for a particularpatient's dosage requirements. Instead of these data being inputted viaa keyboard the pharmacist prepares the programming bar code and appliesit to the syringe, when he has filled the syringe, in dependence upon aprescription tailored to the patient's requirements and provided by thepatient's physician. The patient mounts the bar coded syringe on thesyringe pump, which programs the computer control means automaticallyvia a bar code reader.

The syringe pump is thereby driven entirely in accordance with thephysician's prescription, which prevents injury to the patient throughhis or her improper operation of the syringe pump keyboard. It ispossible for the patient to modify the dispensing of the medicament tosome extent, for example if a supplemental dose is required, but thephysician's data applied to the syringe by means of a bar code by thepharmacist would limit the amounts and frequency of taking themedicament so as to prevent the patient injuring him or herself.

Hereinbefore it has been assumed that the syringe is always filled withmedicament by the doctor, nurse or, in the latter example, by thepharmacist. There has however been a proposal for drug manufacturers tosupply syringes, pre-filled with their products, for example tohospitals. It would then simply remain for the appropriate hospitalpersonnel to place the pre-filled syringe on a syringe pump, which wouldthen drive the syringe plunger rod at a controllable rate and for acontrollable time, which could be entered via the keyboard by the doctoror nurse in accordance with the patient's requirements. There thus needbe no transfer of medicament from a vial or bottle to the syringe, andmoreover there is no intervention by physician or pharmacist inproviding the medicament-filled syringe or the instructions for its use.

It is an object of the present invention to provide with a syringe,which preferably but not essentially is pre-filled as describedhereinbefore, a data carrier means to carry data relating to amedicament contained, or to be contained, in the syringe, which datacarrier means can be read by a suitably adapted syringe pump to takeinto account the data carried. The data carrier means may be presentwith the syringe when it is sold by the manufacturer of the medicamentand/or the syringe to a hospital or pharmacist for example, which isparticularly advantageous when the syringe is a pre-filled syringe.

According to a first aspect of the present invention there is provided asyringe having data carrier means therewith to carry data relating to amedicament contained or to be contained in the syringe, wherein the datacarrier means comprises an electrically and/or magnetically operabledevice to emit data it is carrying in response to activation by asuitable field applied by an external means.

The syringe may be of a conventional design employing for example acylindrical barrel and a plunger, although it is to be appreciated thatthe invention is equally applicable to alternative designs of syringe.

Thus, any container for medicament which is subjected to positivepressure in use, thereby to deliver the medicament, can qualify as asyringe for the purposes of the present invention.

An example of such an alternative design of syringe could comprise aflexible container, for example a flexible bag or bulb, which ispressurised in use by a cooperable pump to drive medicament from the bagor bulb when contained therein.

According to a second aspect of the present invention there is provideda syringe pump cooperable with a syringe according to the first aspectof the present invention, and comprising activation means to emit afield suitable to cause the electrically and/or magnetically operabledevice with the syringe to emit data it is carrying, the syringe pumpfurther comprising receiving means for receiving the data thus emitted,drive means for operating the syringe to deliver to a patient medicamentwhen contained in the syringe, and control means coupled to saidreceiving means and to said drive means to operate the latter takinginto account data received from the data carrier means by the receivingmeans.

According to a third aspect of the present invention there is provided asyringe according to the first aspect of the present invention whenoperably combined with a syringe pump according to the second aspect ofthe present invention.

According to a fourth aspect of the present invention there is provideda method for automatically identifying a medicament or a property of amedicament, comprising providing with a syringe which contains or is tocontain the medicament, data carrier means comprising an electricallyand/or magnetically operable device to emit data it is carrying, andidentifying said medicament or said property thereof, in response toactivation by a suitable field applied by an external means.

According to a fifth aspect of the present invention there is provided apartially disassembled syringe comprising a barrel, a plunger and afinger grip in an assembled state with the plunger fitting closelywithin the barrel and the finger grip being inserted in an open end ofthe barrel, there being a plunger rod provided separately for subsequentassembly with the plunger, and the syringe being provided with datacarrier means to carry data relating to a medicament contained or to becontained in the syringe, wherein the data carrier means comprises anelectrically and/or magnetically operable device to emit data it iscarrying in response to activation by a suitable field applied by anexternal means.

Syringes according to the first or fifth aspect of the present inventionmay be manufactured and sold, preferably pre-filled, in large numbers tohospitals and pharmacists. There need be no application to the syringesof dosage data and the like, which can be programmed into the syringepump at the point of use depending upon the particular patient'srequirements.

When a syringe as described is mounted on a cooperable syringe pump, themedicament-related data may be transferred automatically or on requestto the control means of the syringe pump. This data may comprise anidentification of the medicament contained within the syringe, and/orits concentration. Other medicament-related data could be employedalternatively or in addition, for example batch number and expiry date.

Since the syringe-mounted data need not be entered to the syringe pumpvia a keyboard for example, the responsibilities of the syringe pumpoperator can be reduced as regards the information to be inputted, andthe data carrier means can operate as a recognition device to ensurethat the correct syringe is mounted on the syringe pump for theparticular application concerned. This eliminates incorrect, andpossibly dangerous, administration as a result of operator error.

Various types of device can be used as the data carrier means inembodiments of the present invention. Preferred embodiments may employelectrically and/or magnetically resonant systems, for example amagnetostrictive system wherein the data carrier device comprises one ormore strips of magnetically biased material, which will mechanicallyresonate when activated by an external source of a magnetic field. Theresonance will be detected by the receiving means of the syringe pump,the value of the resonant frequency detected supplying an item of data.

Alternatively, an electronic transponder could be used which outputsdata bits when activated by a field in the form of an interrogatingpower burst via one or more antennae in the syringe pump.

As far as the magnetostrictive embodiments are concerned, singlemagnetic strips may provide respective discrete bits of informationcorresponding to their individual fundamental resonant frequencies, or asingle magnetic strip can be magnetised to respond to its fundamentalresonant frequency and also, or alternatively, to harmonics of thatfundamental resonant frequency.

Preferably a data carrying device is mounted on or in a projection orother part of the syringe, for example on one side of a finger gripthereof. When the syringe is mounted on a cooperable syringe pump, theprojection may project into a groove or recess on the syringe pump tocooperate with an activation means and receiving means within the bodyof the syringe pump, preferably in the vicinity of the groove or recess.

An advantage with the activatable proposed embodiments of the presentinvention may be that contact and/or relative movement need not betaking place between the data carrier and the receiving means for thedata to be read, leading to good reading reliability. Moreover theoptical cleanliness required with a prior art bar code reader, forexample of the window through which the scanner sees the bar code, isnot a problem. Extraneous matter could in principle however interferewith efficient operation of a bar code reader. Moreover, in the opticalsystem the bar code would have to be accurately positioned rotationallyto align with the reader. Finally, an optical bar code system may becapable of being misused, and may not provide the required safety.

Preferred embodiments of the present invention require no contact orrelative movement during reading, leading to reliability, simplicity andconvenience in operation.

For a better understanding of the present invention and to show how itmay be put into effect, reference will now be made, by way of example,to the accompanying drawings in which:

FIG. 1 shows an assembled pre-filled syringe according to the firstaspect of the present invention;

FIG. 2 shows the syringe of FIG. 1 when mounted on a cooperable syringepump according to the second aspect of the present invention, thereby toprovide a combination according to the third aspect of the presentinvention;

FIG. 3 shows an embodiment of syringe finger grip;

FIG. 4 shows part of a syringe and a cooperative activation/receivingmeans;

FIG. 5 shows another embodiment of syringe finger grip;

FIG. 6 shows the principle of the magnetostrictive effect employed insome embodiments of the present invention;

FIG. 7 explains the principle of a first magnetostrictive data carrierwhich may be used in embodiments of the present invention;

FIG. 8 shows the principle of a second magnetostrictive data carrierwhich may be used in alternative embodiments of the present invention;and

FIG. 9 shows an activating and receiving means for a syringe pump whichis cooperable with magnetostrictive data carriers.

FIG. 1 shows an assembled pre-filled medical syringe comprising acylindrical glass barrel 1 having an open left-hand end wherein isinserted a split annular portion 2a of a plastics finger grip 2,locating lateral projections 2b of the finger grip 2 on the end of theglass barrel 1 such that the projections 2b extend in oppositedirections laterally away from the axis of the cylindrical glass barrel1.

In manual use of the syringe, the glass barrel 1 will be held betweenthe first two fingers of the operator's hand, with the two lateralprojections 2b of the finger grip 2 preventing the syringe from slidingbetween those two fingers.

A data carrier means in the form of an electrically (includingelectronically) or magnetically operable device 2c is mounted near theend of one of the two finger grip projections 2b, and details of thisdevice 2c will be provided hereinafter. Preferably however a device 2cis mounted near the end of each finger grip projection 2b, to provideoperability irrespective of the rotational alignment of the syringe.

A syringe plunger rod 3 is attached at its forward end to a rubberplunger 4 fitting closely within the glass barrel 1, and a Luerconnector 5 is attached to the front end of the glass barrel 1, a rubberstopper 1a sealing that forward end.

The syringe is pre-filled with medicament between the rubber plunger 4and the forward end of the glass barrel 1.

Upon delivery to the hospital from the manufacturer of the medicament,the pre-filled syringe is disassembled to some extent and pre-packaged.The glass barrel 1, the rubber plunger 4, and the finger grip 2 arepacked in a pre-assembled state, with the rubber stopper 1a beinginserted at the front end of the glass barrel 1 to retain themedicament. The plunger rod 3 is packaged alongside the glass barrel 1in order to save axial space in the package.

When it is required to use the packaged pre-filled syringe, the glassbarrel 1 and the plunger rod 3 are removed from the package andassembled together, with the rod 3 being screwed into a thread onplunger 4, and the connector 5 is then fitted by the medical staff. Aneedle (not shown) in the connector 5 pierces the rubber stopper 1a.

When packaged, the pre-filled syringe is provided with various otherprotective components which are not relevant to the present inventionand which are not shown or discussed in detail here.

The particular pre-filled syringe which has been shown and described isthe pre-filled syringe being developed, without the data carrier means2c, for the administration of the intravenous anaesthetic `DIPRIVAN`.

FIG. 2 shows the assembled pre-filled syringe of FIG. 1 when mounted ona syringe pump 6 and with the syringe partly emptied.

The syringe pump 6 comprises control means 7 including a microprocessorwithin the body of the syringe pump 6 and an associated keyboard 7a anddisplay 7b. Various other switches and also alarm indicators areprovided on the body of the syringe pump 6, which will be apparent tothe man skilled in the art and which are not shown here in detail.

The syringe pump 6 comprises at its upper edge a longitudinal trough 9into which the glass barrel 1 of the syringe fits. For simplicity thecontents of the glass barrel 1 are not shown in FIG. 2. A pivotableclamp 10 and a stop 11 together secure the syringe on the syringe pump 6within the trough 9. The clamp 10 prevents mainly lateral movement ofthe syringe, whilst the stop 11 abuts against an upper one of theprojections 2b of the finger grip 2 to prevent axial movement of thesyringe in the forward direction.

The lower lateral projection 2b of the finger grip 2 is provided withthe data carrier device 2c (not visible in FIG. 2) and projects lowerthan the trough 9 into a locating groove or recess 12 therein.

A syringe drive means of the syringe pump 6 comprises a linearlyoperating hooded piston 13 which slides along a smooth locating rod 14extending parallel to the axis of the syringe. The piston 13 is actuatedby a drive motor from within the body of the syringe pump 6, as will beapparent to the man skilled in the art.

When the syringe is mounted on the syringe pump 6 as shown in FIG. 2,the data carrier device 2c is located within the body of the syringepump 6 by means of recess 12. There, it is activated by a suitable fieldgenerating activation means within the interior of the body of thesyringe pump 6, adjacent the recess 12 and external of the syringeitself. The data carrier device 2c thereby emits the data it is carryingas will be described in more detail hereinafter. Also as describedhereinafter in more detail, receiving means within the interior of thebody of the syringe pump 6 and adjacent the recess 12 receive the datathus emitted.

The drive means, including piston 13, for operating the syringe todeliver medicament contained therein to a patient, is operated by thecontrol means 7 taking into account the data received from the syringeby the receiving means and fed to the control means 7. If that datarelates to the medicament in the syringe only, the control means 7 willneed to be programmed fully by an operator using the keyboard 7a anddisplay 7b, as regards for example delivery rate and delivery duration,or target blood concentration where appropriate.

Thus, it is envisaged that the emitted data will contain at least anidentification of the drug contained in the syringe and/or itsconcentration, although this could be extended to include further datasuch as for example the batch number of the medicament and its expirydate. Alternative data could be employed also.

The particular syringe pump which has been shown and described is the3100 syringe pump conventionally manufactured and sold by GrasebyMedical Ltd of Watford, UK without the activation means and thereceiving means. It is to be understood that activation and receivingmeans can also be incorporated into other designs and makes of syringepump.

Although the present invention has been particularly described andillustrated thus far with reference to a pre-filled syringe, it is to beappreciated that the syringe need not be pre-filled for example by themanufacturer, but could be filled for example within a hospital. Thus,the present invention is intended also to cover embodiments of thesyringe wherein there is no medicament in the syringe initially, butwherein it is intended to fill the syringe with a particular medicamentidentified by the data carrier device which is mounted on the syringeduring its manufacture or possibly later.

Turning now to the details of the data carrier device 2c, thepossibility has already been mentioned of employing a transponder with asuitable activation means and receiving means. Such systems areavailable in a variety of packages for other applications and arecommercially available from, for example, the company Texas Instrumentsand are known under the title Texas Instruments Registration andIdentification Systems (TIRIS).

FIG. 3 shows how a transponder 15 mounted on a chip carrier may beconnected to two contrawound aerial coils 16,17 and encapsulated withinthe syringe finger grip 2. Upon receipt of power at an appropriatefrequency by one or both of the aerial coils 16, 17, the transponder 15will emit its pre-programmed data from the same aerial coil or coils.

The system would alternatively operate with a single aerial coil woundaround the axis of the syringe, however the implementation describedabove is preferable, as the aerial coils 16,17 are positioned such thatwhen the syringe is mounted on the pump 6, a coil enters the groove 12in the pump case where the activation means' sending/receiving coil ismounted--reducing the power requirement of the transmitter. In addition,the balanced nature of the aerial minimises the risk of crosstalkbetween other pumps and syringes similarly equipped.

A further system, shown in FIG. 4, for tagging the syringe is envisagedthat utilises a circumferential magnetic ink bar code on a syringe label18, and Hall effect transducers 19 mounted within the pump 6. Magneticink bars 20 are printed on the syringe label 18 such that when thesyringe is mounted on the pump 6 the ink bars 20 lie adjacent to thetransducers 19 mounted within the pump 6.

The transducers are composed of Hall effect devices mounted withinelectromagnets 20. The common magnetic inks, such as those found on bankcheques, behave as soft magnets and may not be relied upon to retainmagnetism for long periods. To read the magnetic label described, thelabel is first magnetised by energising the electromagnets 20 woundaround each sensor. This produces a magnetic field to activate themagnetic ink bars 20. The current within the electromagnets 20 isreduced to zero and the magnetic flux produced by the remnant magnetismwithin the ink bars 20 is sensed by the Hall effect devices oppositeeach ink bar. The presence and absence of magnetic bars 20 may be usedto denote the drug type and concentration.

The sensor system does not have to utilise Hall effect transducers.Alternative technologies are becoming available such as thick filmtransducers that utilise magneto-resistive properties of materials.

Alternatively, as a result of a search for technologies applicable toautomatic syringe identification as just described, well known systemshave emerged that utilise electrical or magnetic resonance. Anelectrically resonant circuit composed of inductance and capacitancewill have a resonant frequency ##EQU1## where L is the inductance of thecircuit and C its capacitance. FIG. 5 shows an inductor wound as twoaerial coils 21,22 in series, connected to each end of a chip capacitor23. The inductor may be conductive ink printed on a carrier filmsuitable for moulding into the syringe finger grip 2, or may beinsulated wire.

The activation means will scan the frequencies of interest bytransmitting power from an aerial positioned near the groove 12 providedfor the syringe finger grips 2b. At the resonant frequency of thecircuit within the syringe, the effective impedance of the transmitteraerial will fall substantially. The fall in impedance can be detectedand the frequency of resonance measured. The control system of the pumpmay thus identify the drug type and concentration by the resonantfrequency of the syringe's circuit.

Alternatively, as the result of a search for technologies applicable toautomatic syringe identification as just described, magnetostrictivesystems such as those disclosed in US-A-4510490 and WO 92/12402 emergedas another possibility. The system incorporates a tag 2c moulded intothe syringe finger grip projection 2b, and a detector (which bothactivates and receives) in the body of the syringe pump 6.

The tag is composed of a thin strip of "electrical" steel ribbonoverlying a thin steel strip of hard magnetic steel of similardimension. In the form envisaged, the strips are approximately 10 mmlong and 2.5 mm wide. The combined thickness of the two strips is about0.5 mm.

A tag constructed in the way described will resonate at radiofrequencies when subjected to an incident magnetic (not electric) fieldat its resonant frequency, e.g. 100 KHz. The resonant frequency isprimarily determined by the dimensions and composition of the electricalsteel strip and the strength of its associated bias magnet. Thus byvarying the length of the electrical alloy strip or the strength of thebias magnet, the resonant frequency may be preset according to thecontents of the syringe.

Electric power transformers are designed such that electrical energy inone winding is transferred to a second winding via a conversion to andfrom an "isolating" magnetic field constrained within a steel core. Theefficiency of the transformer has a high dependence on the energy lostto the core during the conversion of the electrical energy into and outof the magnetic field. This energy is absorbed in eddy currents withinthe steel and elastic stains caused by the expansion and contraction ofthe magnetic domains within the atomic structure of the steel.

These strains act through the magnetostrictive effect, which isanalogous to but smaller than the better known piezoelectric effect. Toreduce the effects of eddy currents, the electrical resistance of thesteel is increased with the addition of silicon. Thus transformer coresteel is very efficient at conducting magnetism, enabling the lowenergy, magnetostrictive properties to be exploited in otherapplications.

The electric power transformer industry has dedicated much resource toimprovements in the conversion efficiency of its products. Inparticular, improvement has been gained through the use of bettermaterials in the transformer core. Eddy current losses have been reducedby increasing the resistance of the steel without reducing magneticpermittivity. Some of these high resistance, high permittivity steelsexhibit significant magnetostriction making them suitable for use asresonators in the current application.

Referring to FIG. 6, the magnetostrictive effect is shown by an increasein the length of a steel ribbon when in the presence of a magneticfield. As the field strength is increased, so the ribbon's lengthincreases to the point of saturation (XS). Thus under the influence of afield strength F3 the ribbon has extended by X1. Increasing the strengthof the field to F4 further increases the length by X2.

The U shape of the curve indicates that when the field is reduced fromF1 to zero, reversed and increased to F2, the ribbon will contract to aminimum length at a field strength of zero and extend again by X0 at afield strength of F2. Thus if the magnetostrictive property of theribbon is to be exploited it should be held in a bias field of F4 suchthat it is on the steepest part of the curve. Under the influence ofthis bias field, the material's length will exhibit the greatestsensitivity to any changes in the incident magnetic field strength.

Two systems have been identified in particular which exploit the use ofbiased magnetostrictive materials and which can be exploited aspotential data carrier devices in the form of identification markers forthe syringe. The first uses the fundamental resonant frequency of themagnetostrictive material steel strip and the second employs harmonicsof that resonant frequency. Both systems use a steel strip ofmagnetostrictive material developed for the power transformer industry,biased with a strip of permanent magnet of similar dimensions. The twostrips are sealed and held in a cavity within the syringe finger gripprojection 2b, such that the magnetostrictive element can freely vibratebut is constrained to be in close proximity to or touching the biasmagnet.

Fundamental Resonance System (FIG. 7)

The identification device consists of the two steel strips as describedabove. The steel alloy strip 24 is a magnetostrictive material biased toits sensitive region by the associated magnet 25. When the tag issubject to an incident, additional magnetic field, its length willchange.

If the incident magnetic field produced by the activation means withinthe syringe pump is varying in intensity, the tag will expand andcontract in sympathy with the field. As the incident field frequency isincreased in a scan of different frequencies, a frequency will bereached at which the tag mechanically resonates, expanding andcontracting at an amplitude greater than would be attributable to thepeak values of the incident field alone. This frequency is primarilydetermined by the dimensions of the magnetostrictive strip and itsductility. The resonance may be detected by the receiving means in thesyringe pump as described later.

FIG. 7 shows the standing wave that has formed in the magnetostrictivematerial at the resonant frequency F. At resonance there are null points(no deviation from the mean position) of the wave at the ends of thestrip. Even harmonic frequency waves may also be excited which havenulls at the ends of the strip, although they will be of a smalleramplitude and easily discriminated from the fundamental frequency.

Harmonic Resonance System (FIG. 8)

FIG. 8 shows how the standing wave would form in a magnetostrictivestrip 26 biased with two magnets 27. The first is a 1/4 of the length ofthe strip and the second 1/2 the length. In the proposed system thepairs of poles are "printed" on the same magnetic strip 27 in a similarmanner to the way music is recorded on magnetic tape by cassetterecorders. The manner in which this is achieved will be readily apparentto the man skilled in the art. The strip 26 will have the samefundamental resonance as the strip 24 in FIG. 7. However, in additiontwo strong harmonics may be excited at twice and four times thefundamental frequency. The two magnets 27 could of course alternativelybe separate magnetic strips.

Similar to the fundamental resonance tag, this tag will resonate at itsfundamental frequency as determined by its shape and ductility. However,in addition it may be programmed to resonate at chosen harmonicfrequencies enabling information to be represented by the presence ofabsence of the different harmonics. More harmonics than those showncould be employed.

A fundamental resonance system as described has already been proposedfor example in US-A-4510490, while a harmonic resonance system hasalready been proposed also, for example in WO 92/12402. These previouslyproposed resonance systems could be employed in embodiments of thepresent invention.

Resonance Detection System (FIG. 9)

FIG. 9 shows a circuit designed to act as the activation means and thereceiving means within the body of the syringe pump 6. It will detectthe resonant frequencies of the two magnetostrictive tag systemsdescribed above, and employs the heterodyne principle of received signalprocessing.

A microprocessor 28 of the activation/receiving means is shown coupledto the syringe pump control means 7, which is in turn shown coupled tothe syringe drive means comprising the piston 13.

To eliminate set up costs during manufacture the microprocessor 28calibrates the local oscillator frequencies of oscillator 29 at the"pulse counter" input 30, against its own quartz crystal clock each timethe system is powered up. Following this self calibration, themicroprocessor 28 will have access to a table of all the resonantfrequencies of interest and the "frequency set" voltages required forthe local oscillator to detect them.

Detection of a resonant frequency is initiated by the microprocessor 28setting the appropriate local oscillator frequency and triggering apulse from the pulse generator 31. The pulse will have a duration ofhalf the period of the resonant frequency of interest. The currentresulting from the pulse will cause a magnetic field to be formed aroundthe aerial coil 32, which is mounted within the syringe pump 6 in closeproximity to the tag 2c when the syringe is mounted on the syringe pump6.

In response to the magnetic pulse, the magnetostrictive element of thetag will distort and relax. However, if the pulse duration is 1/2 thewavelength of a resonant frequency, the tag will continue to resonateafter the pulse. The vibration of the magnetostrictive element withinthe magnetic field of its bias magnet will cause a very weak,oscillating magnetic field to be emitted from the tag.

This weak field will generate a current in the aerial 32 which isamplified and fed to the mixer stage 33 of the detector. The mixer 33will produce the difference frequency of the received signal and thelocal oscillator 29. The difference frequency is fed to a two stage,very narrow, bandpass amplifier 34, 35. Thus by choosing the appropriatelocal oscillator frequency, the difference frequency should be thecentre frequency of the bandpass amplifiers 34, 35. Any signal receivedby the aerial 32 of the correct frequency will receive significantamplification by amplifier 36. A signal is taken from each of the threeamplifiers 34, 35, 36 to the signal strength amplifier 37. The resultantsignal strength is fed back to the microprocessor 28.

By comparing the signal strength before the pulse (but after the localoscillator frequency has been set) with that immediately following thepulse, the microprocessor 28 can be programmed to determine whether aresonance was present. The process is repeated for each frequency ofinterest.

The activating and receiving system described above is not the simplestimplementation possible. Simpler systems could be developed whichutilise separate transmit and receive coils enabling continuoustransmission of the exciting field. This method is used in shop doorsecurity systems. However, it is preferable that it should be possibleto fit the same design of activating and receiving circuitry into anumber of different manufacturers' syringe pumps. In this respect thesingle coil system places less mechanical constraints on the syringepump than does a double coil system, and is therefore preferable.

Each detected resonance or harmonic may provide one item of information.Thus, for example, detection of two different fundamental resonancesfrom two strip devices according to FIG. 7 could provide anidentification of a particular medicament and its concentration, ascould the detection of say a fundamental resonance and a harmonic, ortwo harmonics, from a single strip according to FIG. 8.

There have been disclosed embodiments of the invention wherein a syringeis provided with one or more data carrier devices to carry data relatingto a medicament contained or to be contained in the syringe. Preferably,the syringe has two data carrier devices mounted on opposite sides ofthe syringe so that at least one of the devices will always be able tocooperate with an activation/receiving means provided within the syringepump.

Preferably two data carrying devices are provided in the respectiveopposite finger grip projections of a syringe finger grip.

However, embodiments such as those shown in FIGS. 3 and 5 need only haveone data carrying device (transponder 15 or chip capacitor 23) and theuse of two aerial coils on the two finger grip projections makes thispossible.

For safety, the or each data carrier device should not be insertableinto a syringe by the user, and moreover should not be reusable toreactivate the syringe pump after the syringe has been emptied.

To assist in achieving this, the or each data carrier device and anyconnections should be embedded within their surrounding material,preferably by moulding or encapsulation.

Also, the or each data carrying device could be adapted to beincapacitated after one use. In the case of the transponder, it or thepump could be programmed to achieve this. The magnetostrictive tagscould have their bias magnets demagnetised by generating a suitablefield around the detector aerial. The ability to demagnetise the biasmagnet will require a specific choice of material for the bias magnet iferasure is not to occur during transport or storage and yet is not torequire impractical demagnetising field strengths. The man skilled inthe art will be able to make this choice of bias magnet material independence upon the particular requirements of any particularembodiment.

It has however been found that a particularly suitable material for themagnetostrictive strip is Metglas (trade mark) 2605 in most embodiments.

These measures are intended to limit the potential for misuse of eithera pre-filled syringe or a cooperable syringe pump. For example, thepre-filled syringe should not be reused with an alternative medicament,or even re-used with a re-filling of the original medicament.

Moreover the computer controlled syringe pump should not be used with analternative medicament and/or an inappropriate mathematical modelincorporated in its programming.

Although a plurality of data carrier means activatable by suitablefields have been specifically disclosed herein, it is to be understoodthat the present invention is not restricted to these. Any electricallyand/or magnetically operable device suitable for the indicated purposemay be employed in embodiments of the present invention. In particular,it is to be understood that the operation of the data carrier means neednot be wholly electrical and/or magnetic, and thus for example opticaland/or acoustic elements may be employed in conjunction with electricaland/or magnetic devices in alternative embodiments.

It is further to be understood that the invention is not restricted tomagnetic and/or electrical fields to be put into practice. Any othertype of field (electromagnetic or otherwise) which is suitable toactivate a cooperable data carrier means in accordance with the presentinvention can be employed. Thus, in alternative embodiments of theinvention for example fields comprising radiation anywhere within theelectromagnetic spectrum may be employed, and also other fields such asacoustic or other non-electromagnetic fields may be employed in suitablyadapted embodiments.

Further, although a preferred location for the data carrier means hasbeen disclosed to be in the finger grip for a syringe, it is to beunderstood that in a syringe specifically intended for use with asyringe pump, projections 2b in FIG. 1 may no longer be intendedactually to be used as finger grips. Nevertheless, this has been aconvenient manner in which to describe projections 2b in the presentdocument, and it is to be understood as being non-limiting.

It is also to be understood that the data carrier means could be locatedelsewhere in or on the syringe for example on a label as shown in FIG.4, or embedded or molded within the syringe barrel 1, or on or in someother specially-provided additional part or projection not specificallydisclosed herein.

I claim:
 1. A syringe having data carrier means to carry data relating to a medicament associated with the syringe, wherein the data carrier means comprises a device which is operable in at least one of an electrical mode and a magnetic mode to emit data in response to activation by an activating signal applied by an external means.
 2. A syringe according to claim 1, wherein said data carrier means is a resonant device.
 3. A syringe according to claim 2, wherein the resonant device is a magnetically operable magnetostrictive device.
 4. A syringe according to claim 3, wherein the magnetostrictive device comprises at least one element of magnetically biased material, which will mechanically resonate when activated by an external source of an activating magnetic field.
 5. A syringe according to claim 4, wherein the magnetostrictive device comprises at least one strip of magnetostrictive material biased with at least one strip of permanent magnet.
 6. A syringe according to claim 3, wherein the magnetostrictive device is adapted to resonate at at least one fundamental frequency.
 7. A syringe according to claim 3, wherein the magnetostrictive device is adapted to resonate at at least one harmonic frequency.
 8. A syringe according to claim 1, wherein the data carrier means comprises an electrically operable transponder device.
 9. A syringe according to claim 2, wherein the resonant device is an electrically operable resonant circuit comprising inductance means and capacitance means.
 10. A syringe according to claim 1, wherein the data carrier means comprises an aerial means to receive said activating signal and to emit data.
 11. A syringe according to claim 1, wherein the data carrier means is adapted to be incapacitated after one use so that the syringe cannot be reused.
 12. A syringe according to claim 1, which is provided with a plurality of said data carrier means.
 13. A syringe according to claim 1, wherein the data carrier means is embedded with surrounding material of the syringe.
 14. A syringe according to claim 1, wherein the data carrier means is mounted on a projection of the syringe.
 15. A syringe according to claim 10, wherein said aerial means is distributed around the syringe.
 16. A syringe according to claim 14, wherein the data carrier means is mounted on a lateral finger grip projection of the syringe.
 17. A syringe according to claim 16, wherein the syringe comprises two finger grip projections at opposite sides of the syringe, and each finger grip projection has mounted on it a respective said data carrier means.
 18. A syringe according to claim 1, which is pre-filled with medicament.
 19. A syringe according to to claim 1, which is empty.
 20. A syringe according to claim 1, wherein said data identifies the concentration of said medicament associated with the syringe.
 21. A syringe according to claim 1, comprising a cylindrical barrel and a plunger which are cooperable to drive medicament from the syringe when contained therein.
 22. A syringe according to claim 1, comprising a flexible container which in use is pressurised by a cooperable syringe pump to d rive medicament from the container when contained therein. 